Fuel cells are well known and are commonly used to produce electrical energy from hydrogen containing reducing fluid and oxygen containing oxidant reactant streams to power electrical apparatus such as motors, and transportation vehicles, etc. A fuel cell power plant may include a plurality of fuel cells arranged in a well known cell stack assembly along with various support systems, such as hydrocarbon fuel processors, thermal management systems, etc. In fuel cell power plants of the prior art, it is known that a sudden increase in an electrical load on the plant may result in an inadequate amount of hydrogen fuel within fuel cells of the plant. Failure to supply adequate hydrogen to the fuel cells of the plant results in many problems, including corrosion of common carbon support materials that support electrode catalysts. Such corrosion quickly leads to irreversible damage to fuel cells of the plant.
Known methods to maintain an adequate supply of hydrogen within an anode flow field of a fuel cell include use of a burner to combust unused hydrogen passing out of the fuel cell through a fuel exhaust. A temperature of an effluent from the burner is directly related to an amount of hydrogen within the fuel cell exhaust stream. The temperature is sensed and communicated to a controller for varying a rate of hydrogen fuel and/or air being fed into the fuel cell or a fuel processor, to thereby facilitate provision of an adequate amount of fuel to the fuel cell. For example, if the temperature of the burner effluent were to decline, a rate of hydrogen flow into the fuel cells would be increased. Burners, however, increase a cost and volume of a fuel cell power plant. It is also known to utilize a membrane electrode assembly having fuel inlet and exhaust gas streams of a fuel cell passing adjacent opposed sides of the assembly to detect a fuel concentration differential between the fuel inlet and exhaust streams, and to communicate the fuel differential to a controller to regulate a flow of fuel within the fuel inlet stream, such as disclosed in U.S. Pat. No. 6,455,181 that issued on Sep. 24, 2002. The detector in such a system is a voltmeter that detects slight variations in a voltage across the membrane electrode assembly resulting from differences in composition between the fuel inlet and exhaust stream.
Such known systems, however, rely upon measurement of a sensitive voltage differential that is subject to influence by many variables of an operating cell including a membrane electrode assembly. For example, the temperature and dew point of the fuel inlet stream will be considerably different than the temperature and dew point of the fuel exhaust stream. A result of the differential in temperatures and dew points of the fuel streams can result in condensation of water within the cell that can lead to blockage of flow channels or flooding of diffusion layers adjacent the membrane electrode assembly, all of which will negatively impact the voltage detected across the membrane electrode assembly. Additionally, a PEM electrolyte of a membrane electrolyte assembly must not be allowed to dry out if it is to provide reproducible performance of the sensor cell. Accordingly, there is a need for a fuel cell power plant having enhanced control of supplying fuel through fuel cells of the plant.